The use of spectacle lenses for the correction of ametropia is well known. Typically, a polymeric article, conventionally known as a lens blank, is manufactured by casting or machining, which blank has a first surface having at least one refractive power. The second surface of the blank is then machined to provide what is known as an “uncut lens”, the second surface of which has at least one additional refractive power. Prior to machining of the second surface, the diameter of the blank or uncut lens typically is reduced by cutting to a round shape, which cutting process is known as cribbing.
The machining of the second surface can result in formation of a sharp edge at the periphery of the uncut lens. The sharp edge is disadvantageous in that it is prone to cracking or chipping resulting in one or both of contamination of subsequent cleaning or coating steps of the manufacturing process and an unusable uncut lens. Additionally, the sharp edge makes the uncut harder to handle either manually or by machine. Finally, uncut lenses with sharp edges are more likely to exhibit coating defects and be rejected as unacceptable from a cosmetic basis.
In conventional lens manufacturing processes, any sharp edge that remains after machining is eliminated by hand-filing or grinding of the edge. Alternatively, the periphery of the blank or uncut lens may be cut, or cribbed, to an elliptical shape to eliminate the sharp edge. These methods are disadvantageous in that they either add labor and, thus, cost to lens production or the sharp edges are not eliminated in all cases.